1. Field of the Invention
The present invention relates to improvements in an operation control lever unit for regulating power of an engine of an engine-powered working machine, such as a portable bush cutter, to control operation of a working tool of the working machine.
2. Description of the Related Art
Typical examples of known operation control lever units of the type concerned are disclosed in Japanese Patent Publication No. SHO 57-21962, entitled "BUSH CUTTING MACHINE WITH SAFETY DEVICE" and Japanese Utility Model Publication No. 57-42261, entitled "CUTTER BRAKING DEVICE FOR BUSH CUTTER".
The bush cutting machine disclosed in Japanese Patent Publication No. SHO 57-21962 includes an operation control lever unit having a throttle lever and a brake release lever pivotally mounted on an upper end portion and a lower end portion, respectively, of an operation handle in such a manner that areas of pivotal movement of the two levers overlap with each other. The operation handle is continuously gripped with a hand of the operator during operation of the bush cutting machine. During that time, the throttle lever is depressed by the index finger to adjust power of an engine of the bush cutting machine while the brake released lever is held in its fully depressed position using the middle, third and little fingers so as to keep the a circular cutter free from braking force. When a grip on the operation handle is released, the brake release lever returns to its original braking position during which time the free end of the brake lever comes into engagement with a free end of the throttle lever, then forcing the throttle lever to return to its original throttle full-close position (idling position).
In the disclosed operation control lever unit, since the throttle lever and the brake release lever are both provided on the same side of the operation handle, all the fingers of the operator's hand should be used for manipulation of the two levers (including frequent depressing and releasing of the throttle lever) while keeping the necessary grip on the operation handle. This operation exerts a great load on the fingers of the operator's hand, making it difficult to continue the bush removing work for a long time while keeping a desired position of the circular cutter. The conventional bush cutting machine is therefore unable to achieve a high working efficiency.
The bush cutter disclosed in Japanese Utility Model Publication No. 57-42261 includes an operation control lever unit having a throttle lever pivotally mounted to an upper portion of an operation handle, and a brake release lever rotatably mounted to a lower portion of the operation handle in symmetric relation to the throttle lever about the axis of the operation handle. In use of the bush cutter, the operation handle is gripped with one hand of the operator in such a manner that the throttle lever and the brake lever can be manipulated by the index finger and the palm, respectively of the same hand. To place the throttle lever in the operative condition, the brake release lever is turned about the axis of the operation handle in one direction to release a brake mechanism acting on the power transmission line between an engine and a circular cutter of the bush cutter. This operation requires the operator to bend the wrist while keeping a sufficient grip on the operation handle.
The disclosed operation control lever unit has a drawback that since operation of the brake release lever requires bending of the operator's wrist, the wrist soon becomes fatigued and sometimes is damaged. Bending of the wrist may further limit variations in the posture available for the circular cutter during bush cutting operation. Additionally, if the operator unintentionally unbent his wrist while depressing the throttle lever, the brake release lever is allowed to return to its original braking position, thus forcibly terminating the throttle adjusting operation.
Furthermore, since the fulcrum of each lever is disposed exteriorly of the operation handle, both of the conventional operation control lever units are defective from the asthetical point of view.